This project is designed to apply a multi-disciplinary approach to study the relationship between microcirculatory flow dynamics and solute exchange in microcirculatory beds. Preparations of living perfused tissues are studied on a specially designed intravital microscope capable of observations on patterns of distribution of microvessels as well as detailed local observations of flow velocity, vessel diameter, and, by use of fluorescent tracer techniques, of transvascular and interstitial transport of fluorescence-tagged macromolecules. Fluorochromes are stimulated by monochromatic laser illumination in incident light, and observed and recorded by a high sensitivity closed circuit television system. Quantitative analysis is carried out by digitization of data carried on the video record, permitting spatial relationships to be evaluated at several regions in the same experiment. The system permits study of surface vasculature of opaque organs as well as those subject to transillumination. Regions of particular interest, as identified by intravital microscopy, are fixed and subsequently studied by electron microscopy. The ultimate goal is to improve both quantitative and qualitative understanding of solute exchange between the microvasculature and tissue.